1. Field of the Invention
The invention generally relates to a system for generating and transmitting a telemetry formatted message containing raw Global Positioning System (GPS) positional information, processed Inertial Measurement Unit (IMU) attitude information corresponding to a vehicle experiencing high dynamic motion. In addition to GPS and IMU information, events tagged with GPS time are formatted for telemetry output to a ground receiving station. The GPS and IMU telemetry formatted message is received by the ground receiving station and used to improve Kalman filter operation. In particular, the GPS and IMU telemetry formatted message is used as an input to a ground based Kalman filter that is set to track and predict the trajectory of the vehicle, necessary for fast tracking acquisition. The GPS and IMU telemetry formatted message content improves the overall operation of the Kalman filter by preventing Kalman filter resets that occur when a bit error is encountered in IMU data and improves the time correlation of high data rate IMU information and low data rate GPS information, both necessary for accurate tracking of the vehicle experiencing high dynamic motion.
2. Description of the Prior Art
Historically, time, space, position information (TSPI) information was obtained from radar tracking data, laser tracking data and optical tracking data. Global Positioning System (GPS) instrumentation systems have been developed and are widely used to derive TSPI data from GPS information transmitted from a vehicle and received by a ground station. TSPI data is derived by processing the GPS information and feeding vehicle positional updates into a Kalman filter which derives a track and a trajectory prediction for the vehicle.
Another method to obtain an even higher degree of accuracy in reported positional information requires the high speed vehicle to transmit raw GPS data and raw IMU data to a ground receiving station where ground based signal processing can be applied to time correlate the GPS and IMU data. Once time-correlated the GPS and IMU data may be used as an input to a Kalman filter for tracking and trajectory prediction. One disadvantage to correlating the IMU and GPS data and then feeding them concurrently into a Kalman filter is that an IMU bit error will reset the Kalman filter. Multiple IMU bit errors inducing multiple wait states in the Kalman filter degrades tracking accuracy. Another disadvantage of combining GPS and IMU data is the inherent difficulty in time correlating the high rate IMU data with the low rate GPS data at the receiving station.
This invention presents a solution to the problems of degrading tracking accuracy in the presence of IMU bit errors overcomes the inherent difficulty in time correlating GPS and IMU data by implementing an onboard vehicle message formatting system to improve ground station tracking accuracy derived by a Kalman filter. This improved tracking accuracy provides faster tracking acquisition time for a vehicle in high dynamic motion.